Laserfiche WebLink
06 November 2002' - - <br /> AGE-NC Project No. 95=01.73 <br /> Page 2 of 3 '•; i I <br /> - Besides Hydrologic Unit 1,:AGE identified another hydrologic flow unit (Hydrologic Unitr 2)Jn. <br /> October 2001 between 38 and 65 feet bsg(Cone Penetrometer:Testing Site Inv'estigdtion-Fourth <br />' Quarter 2001, dated 19 February 2002)."Based on petroleum concentrations encountered in water <br /> samples collected in this interval from wells AWA and-AW-2,'corrective action is warranted at the <br /> site in Hydrologic Unit 2 (38 feet to .65 feet.bsg)Jn the area between wells'IAW-1 and AW-2.' <br /> However, due to the slow-pace and marginal effectiveness of IAS currently bung encountered in <br /> Hydrologic Unit 1, and due to the unfavorable lithology change between Hydrologic Unit I (less <br /> permeable silts and silty sand) and Hydrologic Unit 2 (more permeable fine to medium sand), IAS r <br /> will probably not be the optimal remediation alternative to address Hydrologic Unit 2 because ofthe' ' <br /> high potential for-air flow channeling.A geologic cross section(C-C) is illustrated iii_Figure 3 that: r _ <br /> depicts Hydrologic Units 1 and 2. <br /> Based on the well-defined,•laterally continuous, sandy nature-of Hydrologic Unit 2Jt would appear <br /> advantageous to implement-a groundwater extraction system screened through Hydrologic Unit.2; <br /> additionally, a ground water pump-and-treat system may, augment they IAS clean-up efforts-in " <br /> Hydrologic Unit 1. Subsequently, AGE.proposed in the-29 April 2002 Work Plan Addendum:tliat 4 <br /> an on-sife ground water extraction-well.be installed utilizing a screen interval b'etw_eeri 30 feet and- <br /> 60 feet bsg (Hydrologic Units 1 and <br /> r In the 19 July 2002 meeting,-the SJCEHD requested that, since Hydrologic-Unity 1 was being i <br />_ . remediated with SVE/IAS technology, the ground water extraction well.should be screened solely <br /> in Hydrologic Unit 2, at between 38 and 65.feet bsg. SJCEHD and AGE concurred that utilization _ <br /> of a ground water pump-and-treat technology in Hydrologic Unit_ 2 would inhibit further migration' <br /> of petroleum hydrocarbon-impacted,--ground water_ off-site (implement hydraulic control),. <br /> immediately reduce the mass of the existing plume,and provide immediate relief and-protection for. ' <br /> the municipal drinking water well located-only 650 feet toward-the northeast (downgradierit) of the <br /> site. Therefore, AGE recommends the following revisions to.the Work-Plan Addendum (dated29 <br /> April 2002). <br /> 1. The proposed ground water extraction well screen'interval should be placed at between <br /> 40 feet and 65 feet bsg:(screened solely through Hydrologic Unit 2): <br /> 2. Following installation of the groundwater extraction well, a 487h1 our aquifer pumping test' <br /> should be performed:at the site to predict.a general ground waterradius of influence and, <br /> capture zone during ground water extraction.".The first-24-hours should be utilized for a step <br /> 4 draw-dawn pump test'(pumping rate incrementally raised at regular intervals)to evaluate the <br /> efficiency and sustainable yield of the pumping well;AGE recommends'starting the test-at <br /> 2 gallons per minute(GPM) and.increasing the extraction rate 2 GPM every four hours.'The <br /> second 24-hours should be.utilized for a constant rate pump test:: <br /> 3. Results of the step draw-down test and aquifer pumping test will^be presented in a report:of 5_ <br />- ' findings-based on the results of the aquifer pumping test,AGE will make'recoinmendations <br />